Electrical devices such as fault circuit interrupters are typically installed into a wall box. Wall boxes which can also be called electrical boxes are typically installed within a wall and are attached to a portion of the wall structure, such as vertically or horizontally extending framing members.
Typically, the depth of the wall box is constrained by the depth of the wall and/or the depth of the wall's framing members. Electrical wiring is typically fed into a region of the wall box for electrical connections to/from the electrical device(s) resulting in a portion of the wall box's volume/depth being utilized by this wiring, while the remaining volume/depth of the wall box is utilized by an installed electrical device. Since normal installation of electrical devices is typically constrained by the distance in which they may extend beyond the finished wall surface, the greater the depth of the housing of the electrical device, the harder it is to fit an electrical device within the constraints posed by the electrical wall box and the finished wall surface. Wall boxes are typically configured to receive two electrical connections, one for line and the other for load, each containing a hot/phase wire, a neutral wire and a ground wire, for a total of five or even six wires being fed/connected into the wall box.
In many cases, circuit interrupters are incorporated into single gang electrical devices such as duplex receptacles, a switch or combination switch receptacles.
Single gang electrical enclosures, such as a single gang wall boxes, are generally enclosures that are configured to house electrical devices of particular heights, widths and depths. In many cases, single gang metallic boxes can vary in height from 2⅞″ to 3⅞″ and in width from 1 13/16″ to 2″, while single gang non-metallic boxes can vary in height from 2 15/16″ to 3 9/16″ and in width from 2″ to 2 1/16″. Therefore, for purposes of this disclosure, a standard single gang box would have a width of up to 2½ inches. A non standard single gang box would have a width of even larger dimensions up to the minimum classification for a double gang box, and any appropriate height such as up to approximately 3⅞″. It is noted that the width of a double gang box is 3 13/16 inches according to NEMA standards. See NEMA Standards Publication OS 1-2003 pp. 68, Jul. 23, 2003.
Due to the space restraints, and because of the complexity of electrical designs of fault circuit interrupter designs in general (i.e., circuit interrupters typically include a number of electrical components), circuit interrupter designs based upon the present state of the art do not allow for much reduction in the depth of the device.